Invasive species are organisms that are not native to a particular ecosystem and whose introduction causes or is likely to cause harm to the environment, economy, or human health. These species often outcompete native organisms, disrupt food chains, and alter habitats, leading to significant ecological and economic consequences. The green iguana (Iguana iguana) serves as a prominent example of an invasive species in various non-native regions, particularly in places like South Florida and Puerto Rico. Their establishment in these new environments has resulted in numerous negative impacts, affecting both natural ecosystems and human infrastructure.
Iguana Traits Supporting Invasion
Green iguanas possess several biological and behavioral characteristics that enable them to thrive and spread rapidly in new environments. They exhibit a high reproductive rate, with females laying clutches of 20 to 71 eggs once per year. This prolific egg-laying capability contributes to rapid population growth in areas where conditions are favorable. Females typically burrow up to three feet deep to lay their eggs, and the eggs hatch during the wet season, approximately 90 to 120 days after being laid.
Iguanas are primarily herbivores, consuming a wide range of plants, including leaves, fruits, and flowers. While primarily plant-eaters, juvenile iguanas may also consume insects, and adults have been observed eating tree snails, small vertebrates, and bird eggs. This generalist diet allows them to adapt to diverse food sources available in different habitats. They are highly adaptable, inhabiting various environments from urban areas to natural ecosystems, including rainforests, dry forests, savannas, and even coastal regions near water.
In non-native regions, green iguanas often lack the natural predators and diseases that regulate their populations in their native Central and South American ranges. Their physical characteristics also contribute to their success; they are large lizards, with some males reaching over six feet in length and weighing up to 17.5 pounds. Their strong limbs and sharp claws are well-suited for climbing, and they are also excellent swimmers, able to dive into water to escape threats. Their burrowing habits further aid their establishment and can lead to property damage.
Ecological Disruptions Caused by Iguanas
The presence of green iguanas in non-native ecosystems leads to significant disruptions of native flora and fauna. Their herbivorous diet poses a threat to native vegetation, including rare and endangered plant species. For instance, in Florida, they consume plants like nickerbean, which is a host plant for the endangered Miami Blue butterfly, hindering the butterfly’s ability to re-colonize areas. They also damage agricultural crops and ornamental plants.
Iguanas compete with native wildlife for essential resources such as food and basking sites. This competition can displace or outcompete indigenous species, impacting the delicate balance of the ecosystem. While primarily herbivorous, there are documented instances of adult iguanas preying on bird eggs and small lizards, further threatening vulnerable native populations. Their burrowing activities can destabilize natural habitats, disrupting ecological processes and potentially damaging the burrows of native species like the Florida Burrowing Owl or gopher tortoise.
Iguanas also pose a risk of disease transmission. They are known carriers of bacteria such as Salmonella, which can be transmitted to native wildlife or humans through contact with contaminated water or surfaces. While scientific evidence regarding large-scale transmission to wild populations is still developing, the potential for impact remains a concern. The accumulation of their droppings in natural areas also contributes to unsanitary conditions.
Infrastructure and Property Damage
Green iguanas cause direct physical damage to human structures and property, creating tangible problems for residents and businesses. Their extensive burrowing is a significant concern, as these tunnels can undermine the structural integrity of seawalls, foundations, sidewalks, and driveways. This activity can lead to costly repairs and compromise the stability of various built environments. These burrows can also affect septic systems and canal banks.
Beyond structural damage, iguanas are known to devastate landscaping and gardens. They consume a wide array of ornamental plants, flowers, fruits, and vegetables, leading to considerable losses for homeowners and commercial growers. Preferred plants include hibiscus, orchids, roses, and various garden greens. This destructive feeding behavior necessitates protective measures or costly plant replacement.
Utility interference is another issue, as their presence near power lines or underground conduits can lead to damage. The large amounts of droppings iguanas leave behind create aesthetic and sanitary problems. These droppings can contaminate swimming pools, patios, and docks, posing a nuisance and potential health hazard due to the presence of bacteria like Salmonella.
The Path to Invasion: How Iguanas Spread
The primary mechanism for the introduction of green iguanas into non-native regions is the exotic pet trade. Many iguanas are purchased as small, docile pets but grow rapidly, reaching large sizes that many owners are unprepared to manage. This often leads to escapes or intentional releases into the wild by owners who can no longer care for them. Once released, these individuals can establish breeding populations if conditions are suitable.
Accidental transport also contributes to their spread. Iguanas have been known to hitchhike on cargo, vehicles, or boats, inadvertently traveling to new territories. This unintentional movement allows them to bypass natural geographical barriers. For example, some initial populations in the Florida Keys arrived as stowaways on fruit-carrying ships.
Once established, iguanas can naturally disperse to new areas through their own movement. Females may migrate considerable distances to find suitable nesting sites, and hatchlings can also spread across landscapes. The tropical or subtropical climates found in many invaded regions, such as Florida, are highly conducive to their survival and reproduction, mimicking their native habitats. The warm temperatures and abundant vegetation allow them to thrive, with populations quickly increasing in the absence of natural controls.